1. Field of the Invention
The present invention relates to a motor drive control apparatus for performing current control of a five-phase stepping motor.
2. Related Background Art
In recent years, with the improvement in speed of a copying machine, a five-phase stepping motor operating stably in a wide speed range has been used, and microstep drive is performed in order to realize high picture quality.
A conventional drive method will be described using a five-phase stepping motor of pentagon connection as an example. FIG. 25 is a block diagram of a conventional five-phase stepping motor drive control. In FIG. 25, a stepping pulse clock (hereinafter referred to as Mclk) for switching a phase is given to a control portion 11, and various driving conditions such as motor starting, rotation direction, and others are instructed. The control portion 11 generates a drive pulse signal in accordance with the Mclk, the pulse signal passes through gate portions 17 and 18 and a Pch electrical voltage converting circuit 313, and a drive section 12 supplies a drive current in accordance with the drive pulse signal to a motor 13 so that the motor 13 is driven.
At this time, in order to cause rotation at a suitable torque, constant electrical current control is made such that a Vref signal from the control section 11, which has been converted into an analog signal by a D/A converter 311, is compared with a motor electrical current detection signal Verr obtained by an electrical current detecting resistor 14, and a voltage Vm corresponding to that is supplied to the drive section 12 to keep an indicated current (FIG. 26).
FIG. 2 is an inner structural block of the drive section 12. In FIG. 2, an FET (Pch, Nch push-pull structure) is used as an element to make a current flow to a motor 13. Since the constant electrical current control is performed, in the case where a counter electromotive voltage in the motor 13 also becomes small when, for example, the motor 13 is driven at a low speed, there occurs a problem that the voltage Vm also becomes small and a gate voltage of a Pch side FET becomes insufficient. Thus, in a Pch electrical voltage converting circuit 313, electrical voltage conversion is performed to gain the gate voltage using a minus power supply (FIG. 27).
Next, a drive signal will be described.
A driving method will be described with reference to a pentagon connection diagram of the motor 13 of FIG. 2. As shown in the drawing, motor coils La, Lb, Lc, Ld and Le are annularly connected, and currents are supplied to respective electrical power supply points A, B, C, D and E from the drive portion 12, so that currents (Ia, Ib, Ic, Id and Ie) flowing through the respective coils are determined.
Here, the coils are connected such that when the respective coil currents (Ia, Ib, Ic, Id and Ie) flow in the directions of arrows, vectors of torques acting on a rotor of the motor 13 by the respective coils become TLa, TLb, TLc, TLd and TLe. The rotor moves so as to stop at a stable point in accordance with the vector direction of a vector-synthesized torque TL of the respective torques.
FIGS. 10A and 10B show vectors of torques by an excitation turn from a four-phase excitation point to a next four-phase excitation point (one step at the full step drive).
Here, when a basic current is I0, in FIG. 10A, excitation is made to realize
Ia=I0, Ib=I0, Ic=0, Id=xe2x88x92I0, and Ie=xe2x88x92I0.
By this, a torque vector TL0 is synthesized (FIG. 11).
In FIG. 10B, excitation is made to realize
Ia=0, Ib=I0, Ic=I0, Id=xe2x88x92I0, and Ie=xe2x88x92I0,
and by this, a torque vector TL1 is synthesized (FIG. 11).
When these excitation patterns are changed from TL0 to TL1, the motor 13 is driven by one step (electrical angle of 36xc2x0) in four-phase excitation. Like this, by changing the excitation patterns so that the synthesized torque is shifted every 36xc2x0, the four-phase full step drive is made. By repeating this operation ten times, the electrical angle rounds (movement of 360xc2x0) and becomes the same excitation pattern as the TL0.
Next, conventional microstep drive control will be described.
From FIGS. 12A and 12B, the displacement of the vector from TL0 to TL1 is due to the shift of only TLa and TLc, and it can be easily inferred that if TLa is gradually decreased and TLc is gradually increased, the vector shifts between TL0 and TL1.
Table 1 shows electrical power supply patterns (Duty control) of the respective electrical power supply points (A, B, C, D, E) when one step from TL0 to TL1 is divided into five parts and the microstep is performed in an arbitrary constant time interval (t0 t5 t0: TL0 t5: TL1), and shows change-over displacements of average currents (Ia, Ib, Ic, Id, Ie) converted from the Duty at respective times. Since the vectors of the changing torques are TLa and TLc and shift on a line as shown in FIG. 12A, the synthetic torque TL is shifted as shown in FIG. 12B, so that the rotor is moved in accordance with TL and the microstep is performed.
However, in the foregoing structure, in order to give a suitable torque in response to a speed, the current control circuit (FIG. 26) (that is, the constant electrical current control section 312) for controlling the total current of the motor must be provided as shown in FIG. 25. Besides, since the motor voltage Vm at a low speed becomes very small, in order to gain the gate voltage of the FET element, a gate circuit using a minus power supply as shown in FIG. 27 (that is, the Pch electrical voltage converting circuit 10313) also becomes necessary. Thus, the circuits become complicated, which becomes a great factor in increasing the costs. Incidentally, FIG. 28 is a circuit block diagram of the control section, and FIG. 29 is a view for explaining the operation of the desire.
The present invention has been made in view of the above circumstances, and has an object to provide a motor drive control apparatus for performing drive current control of a stepping motor through a simple circuit structure.
According to another object of the present invention, a short period is provided between one cycle of duty control of an FET element and a next cycle, and the width of the period is controlled so that the total current of the motor is controlled.
Still other objects of the present invention will become apparent from embodiments described below.